The “grandmother hypothesis” suggests women outlive their fertility in order to help raise grandchildren, thereby strengthening the likelihood that their own genes will survive.

In this scenario, “grandmothers… encouraging their sons to have more children” are driven by a biological imperative, Nichols told AFP.

Even among orcas, scientists have shown that females remain with their male offspring, and probably teach them hunting techniques and where to apply them.

– Evolutionary tinkering –

Another theory says that menopause does not, in fact, confer any advantage in the Darwinian struggle to pass on genes from one generation to the next, but is just an accident resulting in a “mismatch” in the ageing process.

“Different parts of the body are likely to age at different rates, in the same way that some part of a car wear out before others,” Nichols said.

In this argument, modern medicine and nutrition has helped outpace the evolutionary process, extending human life beyond its “natural” limits.

To find out who might be right, Nichols and colleagues examined data from 26 different mammal species, including three tribal or historical human populations. . . .